- fixed the debug framerate calculation / drawing code (consolidated duplicated functions & variables mDelta vs a win-only mDeltaTime, no reason to have two), repositioned it to draw on the bottom left (it was colliding with other debug text for the cache info).
- for debug testing purposes, added a #define override to force the image cache to work with less memory (I've picked 8 megs, which is what the psp seems to use - the normal default on win/linux is 20 megs).